Whenever considering a separation between full citizen and not-yet citizen, please keep this in mind.
So, please do understand in no way do I advocate for the actual separation. I think it'd be disastrous and used as a tool of oppression more than anything, despite my admiration of it in the initial post.
Issues have been reduced to opinions - often argued dishonestly, at the expense of basic facts - which in turn have been reduced to emotions.
It's one thing to think about how an issue affects you personally. It's something else entirely to utterly fail to understand that your hot-button feelings about one or two issues can have huge consequences.
Culture works through connections that increase the degrees of freedom of the system as a whole, not through individual moods and biases.
You can't run a 21st century economy without understanding this, and being able to make pragmatic choices based on it.
The problem is that I can't imagine a real method that can compare. There is no proof that the military way produces good citizens, and every other method ever tried introduces barriers, which usually leads to minorities being excluded.
This set me thinking. The big problem with a mechanism for selecting voters is that the people doing the selecting get to manipulate the contents of the voter pool. In this case, army recruiters. Now not only are you selecting candidates who'l make good soldiers, you're selecting candidates who will vote the way you want them to. Combine that with the power to train and condition those people as you choose during their military service, and expel soldiers that don't tow the line, and you've got the makings of a pretty effective one party state system run for the benefit of the party (the military in this case) and not the citizens.
>"...those noble experiments failed because the people had been led to believe that they could simply vote for whatever they wanted . . . and get it, without toil, without sweat, without tears.”
Now, Heinlein argued for a restrictive vote based on civil service, perhaps best exemplified by another quote from the book “Citizenship is an attitude, a state of mind, an emotional conviction that the whole is greater than the part . . . and that the part should be humbly proud to sacrifice itself that the whole may live.” Despite his strong libertarian beliefs, there wasn't really much in terms of traditional politics that Heinlein promoted as he wrote this, aside from the fact that citizens should work to better their country.
While I don't think restricting the vote is the right answer, I do think this mentality of a full citizen is probably a good one for people to have before they vote. Not an intelligence test, not even an issues test (though also probably an okay idea), but instead just can you be relied on to be thinking about someone besides yourself.
Heinlein doesn't flesh this out much further than "man it'd be great if we cared more for our nation", and I am not smart enough to say what this looks like apolitically either, but it's a nice dream.